Original article Comparison between two lunar situations on emission and larval transport of decapod larvae in the Mondego estuary (Portugal) F. Gonçalves a, *, R. Ribeiro b , A.M.V.M. Soares a,b a Departamento de Biologia, Universidade de Aveiro, 3810-193 Aveiro, Portugal b Departamento de Zoologia, Instituto Ambiente e Vida, Universidade de Coimbra, 3049 Coimbra, Portugal Abstract This study compares the rhythms of larval release of the most abundant decapod crustaceans between the New Moon and the First Quarter. Eurelian field surveys were conducted at a small estuary (Mondego river) on the Atlantic coast of Portugal. All taxa showed tidal and lunar rhythm changes in abundance. The larval emission was very strong during nocturnal ebb neap tides at the First Quarter. Export of zoea did not occur to Rhithropanopeus harrisii. Despite the extensive literature on seasonal abundance, dispersal patterns, larval emission and recruitment of estuarine crabs, little is known about patterns of emission and larval transport in estuaries of Atlantic coast of Portugal, with crepuscular high tides around the quarter moons. The aim of the present study was to compare the larval emission of decapods in the Mondego river estuary, at different lunar situations and during nyctemeral cycles. © 2003 Éditions scientifiques et médicales Elsevier SAS. All rights reserved. Keywords: Emission; Larval transport; Decapod larvae; Nyctemeral cycles; Mondego estuary; Portugal 1. Introduction In temperate environments, most decapod crustaceans re- lease their larvae to the water column during a determined period of the year, when the environmental conditions are favourable.Various studies suggest that the rhythm of release is synchronised with the light-dark cycle, the lunar and/or semi-lunar period, the tidal amplitude and the hour of the high tide (see Amend and Shanks, 1999; Ennis, 1975; Gonçalves, 1991; Paula, 1989; Salmon et al., 1986 and oth- ers). Larval release, and the consequent increase of zoeae I on water mass, occurs mainly between sunset and 24:00 h (local time), during high tide and with a semi-lunar period. This combination is different from region-to-region. For example, in the east coast of United States and Japan, that combination occurs during spring tides (highest amplitude) and the Portu- guese coast, this combination occurs during neap tides (quar- ter moon). Different taxa have been studied and revised, like Uca (Bergin, 1981; Christy, 1978, 1982; Christy and Stancyk, 1982; De Coursey, 1979, 1983; Dittel and Epifaniot, 1982; Lambert and Epifanio, 1982; Salmon et al., 1986; Wheeler, 1978), Sesarma (Saigusa, 1981; Saigusa and Hidaka, 1978), Pinnixa (Brookins and Epifanio, 1985; Christy and Stancyk, 1982; Salmon et al., 1986), Callinectes sapidus (Epifanio et al., 1984; Provenzano et al., 1983; Salmon et al., 1986), Xanthidae (Cronin and Forward Jr, 1982; Forward Jr. et al., 1982; Salmon et al., 1986), Xanthodius sternberghii and Cataleptodius taboganus (Christy, 1986), Uca pugilator, Uca tangeri, Palaemon spp., Crangon crangon, Upogebia pusilla, Anapagurus sp., Panopeus africanus, Pachygrapsus marmoratus and Rhithropanopeus harrisii (Gonçalves, 1991; Paula, 1989) Carcinus maenas (Queiroga et al., 1994, 1997). Thus, the rhythm of emission seems to be correlated with the hour of crepuscular high tide and not with the amplitude of tide (Paula, 1989). Experiences carried out with R. harrisii (Forward Jr. and Lohmann, 1983; Forward Jr. et al., 1982) have shown that crabs coming from a non-regular tidal estuary release their eggs 2 h after sunset, thus suggesting a circadian rhythm. Crabs deriving from a semi-diurnal tidal estuary released their eggs in the beginning of high tide, showing a circatidal rhythm. According to the same authors, crabs can adapt their releasing rhythm to news environmental conditions that dif- fer from the original site. The release occurs synchronised with several environmental conditions (e.g. light and tem- perature). The larval behaviour is fundamental to the dis- * Corresponding author. E-mail address: fjmg@bio.ua.pt (F. Gonçalves). Acta Oecologica 24 (2003) S183–S190 www.elsevier.com/locate/actoec © 2003 Éditions scientifiques et médicales Elsevier SAS. All rights reserved. DOI: 1 0 . 1 0 1 6 / S 1 1 4 6 - 6 0 9 X ( 0 3 ) 0 0 0 3 6 - 5